Safety stop for hoists



1942- K. w. STINSON 2,274,231

SAFETY STOP FOR HOISTS Filed Feb. '7, 1940 NVENTOR A ar/ m ff/ 'rzsorz,

U STATES was .,Karl W. Stinso n, Columbus,

bhio, assignor to Columbus McKinnon Chain Corporation, Tonawanda, N.Y.

Application ma t 7, 1946. S ri 3 7.139

19 Claims.

Myinventionrelatesin general tosafetystops for hoists and in particularto such a stop :for

an electrically. driven hoist having but one brake.

p f It is well known to those skilled in the art that on'hoists having but one brake, such brake isreleased simultaneously with the operation of the control lever in the load lifting direction; of the hoist. Under these circumstances, when the current is interrupted during ,the elevation of a load, the load has a tendency'to overhaul the motor of the hoist by reversing its direction of rotation which, if notcheoked; will allow the load to descend without any control thereof."

to overcome the difliculty above mentionedand toprovide a safety' stop whichwill engage the hoist to prevent downward movement of the load when the current is interruptedduring elevation ofthe-load' f I ;;By means of my inventionit is possible to completely release thebrake at or immediately before the applicationof; current to the motor, since any tendency for theload to reverse the brake drum will be; counteracted thereby makg ing it possible toinitially utilize'substantially all of the power to raise the load with a'resulting reduction of wear on the brake bands.

Another object has been to provide means .for holding saidsafety stop in'neutral or inactive position when the hoist is in its neutral position orwhen'the load is being lowered. n

Another object has been to provide means for compensating for the wear on the stop whereby substantially the same toggle action 'on the stop will be maintained throughout the life thereof.

Another object has been to provide a stop of this .nature'which shall not interfere with the regular design'of the hoist or very'materiallyincrease the costof a hoist equipped therewith. 1 Furthermore, my device does not in any wise interfere with the regular hoist'controls of op}- eration' but is ready instantly to act if'the current fails when a load is being lifted.

The above objects and v The principalobject of my invention has been t 'Fig. 3 is'an enlarged view s pt Fig 4 is an enlarged end elevation showing the pivotal mounting of the safety stop. v

' In the drawing I have shown my invention as showing the safety applied to an electric hoist having a casing I0,

dvantag es have been i accomplished by thedevice shown inthe accompanying drawing, of which:

Fig- 1 is an end elevation of an electric hoist embodying :my invention with the cover re- 3 moved, showing the 7 control mechanism and Fig. 2 s ows an enlarged, fragmentary, end elevation of my device held inits inactive position. 1

the outer; cover of which (not shown) having beenremoved to more vclearly show the parts of the. hoist with which my invention is associated. In Fig. 1, which shows an end elevation of the hoist, l represents the shaft on which the brake drumfI'Zof the hoist is fixedly mounted. This shaft isconnected to theshaft (not shown) of the motor by means of suitable well-known gearing (not shown). Pivotally arranged about v the drum I2 are brake arms l3 and |4,'each provided'with asuitable brake lining i5 for frictional engagement withthe surface of the drum.

i2. The brake arm i3 is mounted upon a pivot pin l6 and the arm His likewise pivotally mounted upon a pivot .pin 20.. These. pins are rigidly carried by the'casing' of the hoist. The brake arms I3 and I4 extend across the hoist and have their ends disposed one on either side of. an operating cam 22 which is carried by the control shaft 2| of the hoist, This cam engageswith adjustable release means 23 carried by each of the arms, as is customaryin hoists. of this type. A rod 25 connects thebrake arms l3 and. f4 and is provided with a spring 24-which serves to keepthe brake linings .|5- normally pressed in contact with the brake drum.

Thecontrol shaft 2| is suitably connected to the shaft (not shown) of the control switch |8 which governs the supply of electricity to the motor. Carried by the control shaft 2| is the control lever 26 of my device. This lever is, of course, rigidly mounted upon the shaft as is the cam 22, and it is provided in customary manner with pull cords30and 3|, whereby it is operated either to its up'positiomas shown in full lines in Fig. 1, or to its downposition, as shown by the broken lines in Fig. 2. As is customary in hoists of this type, the control lever is provided with a centralizing spring. 32 which is disposed about the hub of the lever and has one'end engageable with a pin 33 carried by anupstanding arm 34 formed on the control lever 26 and its other end engageable with a pin 35 stationarily arranged on the housing ofthe hoist and carried by a bracket 36. The control arm is provided with means for delaying, the operation consisting of a .detent .bar having a slot. 4| and slidably mounted uponthepi'n 35. .This detent bar is designed; under certain conditions of operation,

to have its lower end edges engage stops or abutments 42 and 43 formed on the upper surface of the control lever and arranged at each end thereof. When, for instance, the cord is pulled the corner edge at the adjacent end of the lock bar 40 will drop down in front of the abutment 43, as clearly shown in Fig. 1. If the control lever 25 is now moved to its reversing position slowly enough, the said corner edge of the bar will engage the abutment 43 and the bar will thereby be pushed longitudinally on the pin past the center of gravity, allowing its opposite end to fall and contact with the opposite end of the lever where it will be engageable with either of the abutments 43 or 42. However, if the control lever is operated from the position of Fig, 1 faster than that predetermined by the type of motor employed on the hoist, the bar will be moved so that the end of its slot 4| will engage the pin 35 before it has had time to tile upon said pin, as above .described, thereby acting as an abutment between the pin 35 and the surface 43 and locking the lever in such a manner as to prevent immediate reverse movement thereof. If now the tension on the cord 30 is slightly released, the lock bar will be free to rotate clockwise and to have its right hand end fall upon the surface of the right hand end of, the control lever. From this position the control lever may be operated to reverse position by pulling the cord 3! if desired, time enough having elapsed for the motor to come to a standstill. If, however, it is desired to again operate the hoist in the same direction and from the first mentioned locked position, the right hand end of the lock bar which has fallen to engage the right hand upper surface of the control lever, as just above described, will be pushed to the left by engagement of its lower right hand edge surface with the abutment 42 of the lever where it will be in position to again interrupt its too rapid operation of the hoist. Since this control mechanism forms no part of my invention, it will not be further described.

My invention comprises a safety lock lever 44 which is pivotally mounted upon the pivot pin l6 and preferably arranged in a slot formed between the arms 45 of the brake arm l3. This lever is provided with a lock arm 46 and with a release arm 50. The lock arm 46 is provided with a friction brake shoe 5| which is mounted in a recess 52 formed in the arm. The shoe is provided on its exposed face with a working surface 53 preferably of curved formation and fitted to the surface of the brake drum I2. The curved surface 53. preferably has a radius equal to the radius of the brake drum I 2 and when it is in engagement with such surface, as shown enlarged inFig. 3, the rear edge of the surface is located at point 54. A surface 55 is also formed on the exposed face of the shoe which is also preferably curved but in reverse direction and is struck from the axis of the pivot pin l5 and has a length equal to the distance from the point 54 to the axis of the pin, which surface therefore meets and joins the surface 53 at the point 54.

In Fig. 3 I have shown a center line 55 extending from the axis of the brake drum to the axis of the pin l6, and it will be noticed that the point 54 is somewhat removed from the point of intersection of said center line with the periphery 60 of the brake drum, so that as the brake drum tends to rotate in the direction indicated by the arrow in this figure, the friction shoe will be drawn in contact with the surface 60 by reason of the toggle action produced. It is important that the toggle action produced by the shoe upon the surface of the drum be maintained irrespective of the wear upon the face of the friction shoe. For this reason, the curved surface is provided which is arranged back of the point 54 in the direction of oscillation of the arm to its working position. It will be seen that as the shoe wears, the surface v53 may increase in length but the point 54 will be maintained at substantially the same distance from the line 56 when in contact with the drum because of the fact that this point is a part of the surface 55 and will always be at the meeting point of the surfaces 53 and 55. Therefore, change of position of the lever due to wear of the frictional shoe will not alter the position of the point 54, thus maintaining the toggle action substantially the same throughout the life of the shoe.

A torsion spring 51 is provided for keeping the lock arm pressed to the position shown in Figs. 1 and 3. This spring preferably has one of its ends engageable with the back side of the release arm and its other end preferably engageable with the top edge of the brake arm l3. This spring is preferably formed between its ends with cylindrical convolutions 58 which are disposed upon the hub 59 formed on the casing H! of the hoist and bearing pivot pin I6.

As shown in Figs. 1 and 3, the friction shoe of the lock lever is in dragging engagement with the brake drum l2, which drum is rotating in the direction indicated by the arrow in Fig. 1 to elevate the load, the pull cord 30 having been operated to move the control lever 25 to the up position.

Under these conditions, the brake arms are, of course, separated and the shoes carried thereby are out of contact with the brake drum l2. Should the electric current be interrupted for any reason while the operator is pulling on the up cord, the load would normally tend to reverse the direction of rotation of the hoist, as indicated inFig. 3, thereby allowing the load to get out of control. However, when this happens, the friction shoe 5| of my device which has been held in light, non-braking contact with the periphery 65 of the drum by the spring 51 during the elevation of the load, will be immediately drawn by the reverse movement into firm braking contact with the said surface by the toggle action hereinbefore referred to and, therefore prevent any appreciablereverse rotation of the drum.

When the hoist equipped with my device is to be reversed and the load lowered by pulling on the cord 3|, it is of course necessary to prevent the operation of the safety lever. This is accomplished by means of a safety lock connecting rod 6| which is pivotally attached at one end to a pivot pin 62 carried by the control lever. This pin is located above the axis of the control shaft 2| so that as the control lever is oscillated during its operation, the rod will be reciprocated back and forth in a substantially horizontal plane. The outer end of the rod is provided with a collar 63 and an outwardly extending end 64. The release arm 50 of the lock lever is provided with an aperture 65 with which the end 64 of the rod slidably engages. When the control lever 26 is reciprocated to its neutral position as shown in fragmentary manner by full lines in Fig. 2, or to its reverse position, as shown in this figure by the broken lines, the collar 63 of the rod will engage with the curved. shaped surface 56 of the release arm 50 and will serve to push the friction shoe out of contact with the periphery 60 of the brake drum I2, thereby permitting the drum tobe freely rotated in reverse direction 112 through the medium of the'spring 51 where it will rest idly in a position to be ready to be drawn into braking action by the idle downward movement of the hoist. Further movement of the rod 6| as the control lever is moved to its fully up position will not have any braking action upon the safety device but theend 64 will idly move'through the aperture 65 formed'in the release arm 50,

From the foregoing it will be clear that an electric hoist equipped with my invention will sustain the load should the electric power fail during the elevation thereof; and, furthermore, the hoist brake may be completely released before the current is applied to the motor of the hoist owing to the fact that the safety stop will prevent the load from overhauling the motor when the brakes are' released previous to elevating the load. This arrangement not only obviates an added starting load for the motor,

, but increases the life of the brake. j I

Having thus described my invention, what I claim is:

1. A hoist having a load-lift means, power means for raising the lift means, control means for the power means, brake means operable by the control means when out of a raisingposition,

to hold the lift means against movement, safety stop means normally operative and adapted to arrest the lift means upon failure of the power means, and means operable by the control means when in a raising position for disposing the stop means operable, whereby upon failure of the power means when lifting a load the lift means will .be arrested, said stop means being inoperative in other positions of the control;

2. A hoist having a load-lift means, power trol'to "releasethe brake means at the time of starting the operating means. r

4; In anielectricallydriven hoist, the combination with the control lever, the brake drum, the' brake arms, and the power means of the hoist, of a safety stop including a single piece stop lever, and a "brake shoe rigidly carried by said lever, said stop lever being pivotally mounted upon a pivotpin fixed with respect to the axis of rotationof the drum, said lever being so proportioned and positioned with respect to the brake drum that the-drum is free of the safety stop on the up movement of the hoist but will produce a toggle actionbetwe'ensaid shoe and the drum to restrain thebdrum from reverse rotation when the current is accidentally interrupted While the brake arms aredisengaged fromthe drum, and release'means connecting said control lever with said stop for holding said brake shoe in its inoperative position during down movement of the hoistj 5. 'In an electrically driven hoist, the combination with the control lever, the brake drum, the brake arms, and the power means of the hoist, of a safety stop including a single piece stop lever, having a lock arm and a release arm, and

a brake shoe rigidly carried by the lock arm of said lever, said stop lever being pivotally mountedupon a pivot pin fixed with respect to the axis of rotation of the drum, said lever being so proportioned andpositioned with respect to the brake drum that the drum is free of the safetystop on the up movement of the hoist but will produce a toggle action between said shoe and the drum to restrain the drum from reverse rotation when the current is accidentally interrupted while the brake arms are disengage-d from the drum, and release means connecting said control lever with said stop and the release arm means for raising the lift means, control means for the power means, said control means having a raising position, a lowering position, and a neutral position, brake means operable by. the control means when out of the raising position to hold the lift means against movement, safety stop means normally operative and adapted to arrest the lift means upon failure of the power means, and means operable by the control means when in a raising position for disposing the stop means operable, whereby upon failure of the power means when lifting a load the lift means will be arrested, said stop means being inoperative in the neutral and lowering positions of the control. Y

3. A hoist having a load-lifting member, drum means connected to the latter and rotatable in one direction thereby upon lowering-said member, means foroperating the member to lift and lower its load, safety stop means normally operable to arrest the drum means against such rotation upon failure of the operating means, brake means for arresting the drum means and controllable to regulate the lowering of the load, a control for the operating means to start and stop the same, and means associated with the condrum, including a safety lock lever pivotally mounted upon a fixed pivot pin, and a brake shoe carried by said lever, said shoe having a working face engageable with the brake drum, and a curved surface joining said working surface and struck from the center of oscillation of said lever.

8. A safety brake for hoists having a brake drum, including a safety lock lever, and a brake shoe carried by said lever, said shoe having a curved working face having a radius substantially equal to the radius of said brake drum, and a curved surface joining said working surface and struck from the center of oscillation of said lever.

9. A safety brake for hoists having a brake drum, including a safety lock lever, and a brake shoe carried by said lever/said shoe having a working face engageable with the brake drum, and a surface behind said working face extending away from theworking face and struck from the center of oscillation of said lever.

10. safety brake for hoists having a brake drum, including a safety lock lever, and a brake shoe carried by said lever, said shoe having a curved working face havinga radius substantially equal to the radius ofsaid'bra'ke drum, and a reversely curved surface behind said working face struck from the center of oscillation of said lever.

11. A hoist having a load-lift means, power means permanently connected to said lift means for raising and lowering the lift means, brake means for restraining said power means when idle, control means for actuating the powenmeans in either direction, release means actuated by said control means to release said brake means when safety stop means normally operative and adapted to arrest the lift means upon failure of the power means, and means operable by the control means when in raising position for disposing the stop means operable, whereby upon failure of the power means when lifting a load the lift means will be arrested, said stop means being inoperable in other positions of the control means.

12. A hoist having a load-lift member, drum means connected to the latter and rotatable in one direction thereby during the lowering movement, power means permanently connected to said member for operating the same for lifting and lowering its load, stop means normally operable to arrest the drum means against. suchrotation upon failure-of the operating'means, brake means for arresting the drum means and controllable to regulate the lowering of-the load, a control for the operating means to start and stop the same, means associated with the control to release the brake means at the time of starting the operating means, and means operable by the control to free the drum means from the stop means simultaneously'with the operation of the control to lower the load.-

'13. A hoist comprising a brake drum, power means permanently connected to said drum for causing the operation thereof to raise and lower the load and including a control lever, brake arms engageable with said drum for restraining the rotation of said power means when idle, and a safety stop engageable with said drum to prevent lowering of the load upon interruption of the power means, whereby said brake arms may be released from said'drum prior to the rotation of said drum.

14. A hoist comprising a brake drum, power means permanently'connected to said drum for causing the operation thereof -to raise and lower the load and including 'a control lever, brake arms engageable with said drum for restraining the rotation of said power means when idle, a safety stop engageable with said drum to prevent lowering of the load upon interruption of the power means, and means connected with such lever to release said brake arms prior to the actuation' of the power means to raise the 1oad,whereby substantially all of the power will be initially applied to said hoist. v

15. A hoist comprising a brake drum, power means permanently connected to said drum for causing the operation thereof to raise and lower the load and including a control lever, brake arms engageable with said drum for restraining the rotation of said power means when idle, a safety stop engageable with said drum to prevent lowering of the load upon, interruption of the power means, and means operable by the control lever to free the drum from the stop simultaneously with the operation of the power means.

16. A hoist comprising a brake drum, power said power means is actuated in either direction,

means permanently connected to said drum for causing the operation thereof to raise and lower the load and including a control lever, brake arms engageable with said drum for restraining the rotation of said power means when idle, a safety stop engageable with said drum to prevent lowering of the load uponinterruption of the power means, means associated with such lever to release said brake arms prior to the actuation of the power means to raise the load, whereby substantially all the power will be initially applied to said hoist, and means operable by the control lever to free the drum from the stop simultaneously with the operation of the power means to lower the load.

17. A hoist having a load-lift member, drum means connected to the latter and rotatable in one direction thereby during the lowering movement,-power means permanently connected to said member for operating the same for lifting and lowering its load, stop means independent of said power means and normally operable to arrest the drum means against downward rotation upon failure of the power means, brake means for arresting th drum means and controllable to regulate the lowering of the load, a control for the power means to start and stop the same, and means operable by the control to free the stop means from the drum means simultaneously with the operation of the control to lower the load.

18. A hoist having a load-lift member, drum means connected to the latter and rotatable in one direction thereby during the lowering movement, power means permanently connected to said member for operating the same for lifting and lowering its load, stop means independent of said power means and normally operable to arrest the drum means against downward rotation upon failure of the power means, a control for said power means, and a connecting rod pivotally carried by said control and slidably connected to said stop means whereby said stop means 'will be held in inoperative position during lowering of the load.

19. A hoist having a load-lift member, drum means connected to said member and, when free, being capable of having movement imparted thereto by said member in lowering direction, power means connected to said member for operating the same for lifting and lowering its load, stop means independent of said power means and responsive to and operable by the initial portion of such member-imparted movement, said stop means being lockingly engageable with said drum means to arrest the latter against member-imparted movement in lowering direction when said power means fails during lifting movement, a control for said power means operable to hoist and lower the load, said control means being wholly independent of said stop means during the operation of the control means to raise the load, and connecting means as sociated with said control and said stop means, said connecting means being actuated by movement of said control means and having sliding connection with said stop means, whereby to hold the latter away from its responsive position with said drum means upon load-lowering movement of said control means but allowing said stop to act independently of said connecting means upon load-lifting movement of said control means.

KARL W. STINSON. 

